What is The Use Of Using Tag To The Disscussion ?????

Posting tags allows other people to find discussions on particular topics easier. They are basically category/search keywords, so if someone searched say tags and you put "tags" in your tags list for this discussion it would have a much better chance of showing up than had you not. Any may not even show up at all if you don't put any tags, its very important to increase the traffic of your discussions.